The main bearing cap, code 102985, is a precision-machined, highly loaded component of the MAN L21/31 engine that securely retains the main bearing and helps maintain the crankshaft in its specified operating position and alignment. Together with the corresponding bearing housing, the cap forms a rigid support capable of transmitting and distributing the substantial dynamic and combustion-related loads acting through the crankshaft while preserving the bearing geometry and clearances required for reliable lubrication and smooth rotation. Accurate seating surfaces, dimensional stability, correct alignment, and the specified preload of the fastening elements are essential, since even relatively small deviations can influence bearing load distribution, lubricating-oil film formation, crankshaft alignment, vibration, and wear. During inspection and overhaul, the cap, contact surfaces, fastening areas, and associated bearing locations should therefore be checked carefully for fretting, deformation, cracking, wear, corrosion, or other deterioration. By maintaining secure crankshaft support and precise main-bearing alignment, the main bearing cap contributes directly to reliable lubrication, reduced mechanical wear, stable engine operation, and the long-term durability of the MAN L21/31 engine.